Final answer:
The total amount Sophia spends is calculated with the algebraic expression $15 + 3r + 2p, where r is the number of roses and p is the number of tulips. Buying 7 roses and 4 tulips results in a total cost of $44.
Step-by-step explanation:
The algebraic expression to find the total amount of money Sophia will spend on flowers, given any number of roses (r) and tulips (p), is 3r + 2p plus an initial $15 for the mixed bunch. We add the initial cost to the expression representing the cost of additional flowers. So, the expression including the initial cost becomes $15 + 3r + 2p.
If Sophia buys 7 roses and 4 tulips, we substitute these values into our expression: $15 + 3(7) + 2(4) = $15 + 21 + 8 = $44. Therefore, the total cost Sophia will spend is $44.